The recent demonstration of chemokine receptors on neurons known to function as coreceptors for HIV and SIV raises the possibility that the neuropathogenesis associated with HIV/SIV infection is mediated via these receptors. We hypothesize that neuronal damage is determined by the interaction of chemokine receptors on neurons with viral envelope protein or chemokines produced by infected macrophage/microglia in the CNS. Such interactions can either result in aberrant signaling through chemokine receptors or interfere with the binding of trophic factors, either of which may be damaging to neurons. A corollary of this hypothesis would be that the neurons expressing the highest density of appropriate chemokine receptors would be the most susceptible. To test this hypothesis we will: 1) Analyze the regional and cellular distribution of chemokine receptor expression in brains of SIV-infected rhesus macaques at different stages of disease compared to uninfected controls. This will be achieved by immunohistochemistry and in situ hybridization for chemokine receptors (CCR3, CCR5 and CXCR4) followed by quantitative image analysis. Confocal microscopy will also be used to determine if there are morphologic alterations in neurons (e.g. loss of dendritic spines) expressing high levels of chemokine receptors in SIV-infected macaques compared to age-matched controls. 2) Characterize chemokine receptor expression in immediately ex vivo and in vitro populations of neurons, astrocytes, and microglia from SIV-infected and uninfected macaques. This will be achieved by using immunohistochemistry, in situ hybridization, and rt-PCR to quantitate chemokine receptor protein and mRNA expression in ex vivo and in vitro enriched cultures of fetal neurons and astrocytes and sorted microglia and astrocytes from SIV-infected animals at different stages of the disease compared to uninfected controls. 3) Evaluate the effects of chemokine receptor stimulation on neurons and glial cells. This will be achieved by exposing enriched neurons or neurons and astrocytes to: 1) soluble factors from SIV-infected microglia or macrophages in a transwell culture system; 2) chemokines that function through CCR3, CCR5, CXCR4, 3) SIVgpl20, and 4) pathogenic versus inactivated SIV. We will then assess neuronal cultures for cellular injury and induction of apoptosis.